First, reference is made to a method for allocating resources in a broadband wireless access system. A base station allocates resources to each terminal (or MS) taking into consideration a channel status (i.e., Channel Quality Information (CQI)), the amount of delay, throughput, and Quality of Service (QoS) of the MS.
In the broadband wireless access communication system, it is necessary to efficiently allocate resources to each of a number of MSs. The following is a detailed description of a method for scheduling allocation of resources.
In a general IEEE 802.16e communication system, a plurality of receivers (for example, MSs) share one channel (for example, a packet data channel) transmitted from a transmitter (for example a base station (BS)). In this case, a single scheduler performs scheduling. This scheduling method is described below with reference to FIG. 1.
FIG. 1 illustrates an internal structure of a scheduling device of a BS in a general IEEE 802.16e communication system. As shown in FIG. 1, the scheduling device includes M MS queues (i.e., 1st to Mth MS queues 111 to 119), a packet scheduler 120, a subchannel allocator 130, a channel encoder 140, a constellation mapper 150, an OFDM modulator 160, a Radio Frequency (RF) processor 170, and an antenna 180.
First, when the number of MSs which are receiving a service from the BS is M (i.e., when 1st to Mth MSs are present), packet data destined for the 1st to Mth MSs are transferred respectively to the corresponding queues. Specifically, packet data destined for the 1st MS is transferred to the 1st MS queue 111 and packet data destined for the Mth MS is transferred to the Mth MS queue 119. When packet data is stored in the 1st to Mth MSs 111 to 119, the packet scheduler 120 performs a control operation such that resources (for example, single-channel resources) of a corresponding scheduling time (for example, Transmit Time Interval (TTI)) are allocated to a specific MS according to a preset scheduling scheme every TTI. Since a single packet scheduler is used in the general IEEE 802.16e communication system, the packet scheduler 120 shown in FIG. 1 is a single packet scheduler.
The packet scheduler 120 outputs allocation information of an MS allocated to a subchannel in the corresponding TTI to the subchannel allocator 130. Here, the allocation information of the MS allocated to the subchannel in the corresponding TTI is determined according to the scheduling operation.
The subchannel allocator 130 allocates the subchannel to the MS in the corresponding TTI according to the allocation information of the MS allocated to the subchannel in the corresponding TTI output from the packet scheduler 120 and outputs the subchannel allocation information to the OFDM modulator 160.
The channel encoder 140 performs channel encoding on data of the MS determined by the packet scheduler 120 according to a preset channel encoding method determined according to CQI of the MS and outputs the encoded data to the constellation mapper 150.
The constellation mapper 150 performs constellation mapping on the signal output from the channel encoder 140 according to a QPSK scheme and outputs the resulting signal to the OFDM modulator 160.
The OFDM modulator 160 OFDM-modulates the signal output from the constellation mapper 150 according to the subchannel allocation information output from the subchannel allocator 130 and outputs the modulated signal to the RF processor 170. Here, a detailed description of the OFDM modulation operation of the OFDM modulator 160 is omitted herein since the OFDM modulation operation is not directly associated with the packet scheduling operation. The RF processor 170 includes components such as a filter and a front end unit and performs RF processing on the modulated signal from the OFDM modulator 160 and transmits the resulting signal through the antenna 180.
The packet scheduler 120 performs a scheduling operation using a Proportional Fairness (PF) scheme.
Here, a Proportionally Fairness Scheduler (PFS) is used to determine terminals that will use Partial Usage of Subchannels (PUSCs) including distributed subcarriers of the OFDMA system. One frame is divided into a number of scheduling resources. The base station sequentially performs PFS until such resources are all allocated. This process is repeated every frame. According to the PFS result, the base station can allocate one or more terminals to one frame. PFS is a method used to select terminals which maximize the value obtained by dividing the maximum amount of data T_insti according to a channel status at a scheduling time “t” by the average amount of actually transmitted data T_smoothedi as in Mathematical Expression 1.
                                          M            t                    ⁡                      (            t            )                          =                                            T_inst              i                        ⁢                          (              t              )                                                          T_smoothed              i                        ⁢                          (              t              )                                                          MATHEMATICAL        ⁢                                  ⁢        EXPRESSION        ⁢                                  ⁢        1            At any scheduling instantt, the scheduling metric Mi(t) for subscriber i 
Here, the process of Mathematical Expression 1 is not performed when there is no data to be transmitted to the terminals.
The average data amount which is a denominator in Mathematical Expression 1 is calculated each time after resources are allocated as in Mathematical Expression 2. A parameter “TPF” in Mathematical Expression 2 represents the size of a window during which the service can be maintained without receiving data.
                    ⁢          MATHEMATICAL      ⁢                          ⁢      EXPRESSION      ⁢                          ⁢      2                          T_smoothed        i            ⁢              (        t        )              =                            1                      T            PF                          *                  T_inst          i                ⁢                  (          t          )                    +                        (                      1            -                          1                              T                PF                                              )                *                  T_smoothed          i                ⁢                  (                      t            -            1                    )                    
In Mathematical Expression 2, the current transmission amount “T_insti” of all terminals excluding terminals selected at time “t” is “0”.
Table 1 represents QoS of various services. The Unsolicited Grant Service (UGS) is sensitive to transmission delay and the sensitivity of each service to transmission delay decreases in the order given in the table (i.e., the Best Effort (BE) is least sensitive to transmission delay).
TABLE 1ServiceDefinitionApplicationsMandatory QoS ParametersUGSReal-time data streamsT1/E1,Max. Sustained Traffic Rate = Min.Consisting of fixed-sizeVoIP w/oReserved Traffic RatedatasilenceMaximum LatencyPackets issued at periodicSuppressionTolerated JitterIntervalsUplink Grant Scheduling TypeRequest/Transmission PolicyUnsolicited Grant Interval (venderspecific)rtPSReal-time data streamsMPEG videoMinimum Reserved Traffic Rateconsisting of variable-Maximum Sustained Traffic Ratesized data packets thatMaximum Latencyare issued at periodicUplink Grant Scheduling TypeintervalsRequest/Transmission PolicynrtPSDelay-tolerant dataFTPMinimum Reserved Traffic Ratestreams consisting ofMaximum Sustained Traffic Ratevariable-sized dataTraffic Prioritypackets for whichUplink Grant Scheduling Typeminimum data rate isRequest/Transmission PolicyrequiredBEData streams for which noHTTPMaximum Sustained Traffic RateMinimum service level isTraffic Priorityrequired and thereforeRequest/Transmission Policymay be handled on aspace-available basis
The BS transmits information of resources allocated using the above method to MSs through a MAP every frame.
In the case of uplink, such information is transmitted through a UL MAP. The BS can transmits such information through a block allocation scheme in which the BS notifies the MS of a symbol offset, the number of allocated symbols, a subchannel offset, and the number of allocated subchannels or a slot allocation scheme in which the BS notifies the MS of a relative or absolute offset and durations of allocated slots.
Table 2 illustrates the usage of each Uplink Interval Usage Code (UIUC).
UIUCUsage 0Fast-feedback channel1-10Different burst profiles (Data Grant Burst Type)11Extended UIUC 2 IE12CDMA BR, CDMA ranging13PAPR reduction allocation safety zone, SoundingZone14CDMA Allocation IE15Extended UIUC
As illustrated in Table 2, the block allocation scheme is used in fast feedback (UIUC=0), HARQ ACK CH region (UIUC-11 (Extended-2 UIUC) with Type=8), CDMA ranging and BW request allocation (UIUC=12), and PAPR/safety zone allocation (UIUC=13), which should all be allocated to regions prior to regions in which the slot allocation scheme is used.
The slot allocation scheme is used in any other UIUC. When the slot allocation scheme is used in non-Adaptive Antenna System (non-AAS) zones, the start position of an initial region is determined by an allocation start time field in the UL-MAP and the start positions of other allocation regions are determined by immediately previous allocation regions in the UL-MAP (i.e., determined through relative offset values). On the other hand, when the slot allocation scheme is used in an AAS UL zone, the start position of the allocation region is determined by an absolute offset explicitly indicated in the UL-MAP.
In the case of downlink, information of allocated resources is transmitted through the block allocation scheme. Table 3 illustrates the usage of each Downlink Interval Usage Code (DIUC).
TABLE 3DIUCUsage0-12Different burst profiles13Gap/PAPR reduction14Extended-2 DIUC IE15Extended DIUC
The BS performs scheduling on all MSs that have data to be transmitted and received in the corresponding cell to allocate resources to the MSs and broadcasts such allocation information to the MSs every frame.
Each MS needs to read all Information Elements (IEs) in a MAP transmitted every frame to determine whether or not any resources have been allocated to the MS. This method is inefficient in terms of power consumption of the MS.